Many commercial and industrial processes create the possibility for explosions, even the warehousing of combustible dusts and products that release combustible vapors presents such a risk. Such explosions may damage or destroy any structure that is not designed to resist the considerable pressures generated by a dust or vapor explosion. Deflagration vents, blow out panels, explosion panels, or explosion vents have been employed to lessen any damage to a structure housing potentially dangerous processes when an explosive event occurs by allowing the pressure created in such an explosion to escape through deflagration vents to mitigate and even prevent the deformation and/or destruction of the structure. A pressure relief device is a broad term encompassing at least all the venting devices described above. The above described venting practices are particularly effective in the case of explosions that propagate below the speed of sound, a deflagration. Industry standards such as NFPA 68 in the United States and the ATEX directive, used in Europe, and related harmonized standards in Europe and elsewhere establish requirements for such protective measures.
Because a temperature, climate, and/or clean controlled environment is desired, and even required by some processes, deflagration vents have been employed that maintain the environmental integrity of the structure. Such vents in the past have been held in place by magnets, spring mechanisms, re-settable latches, or have been constructed of frangible materials. One type of vent involves a burst panel, such as disclosed in co-owned U.S. Pat. No. 7,950,408 (“the '408 patent”), the entire contents of which are incorporated herein by reference. A burst panel may include a release mechanism configured to hold a panel member against a frame, or may be sealed against a frame in some other fashion.
In an explosion or other event causing a vent to open, it may be desirable to prevent the opened portion of the vent (e.g., the panel in a burst panel vent) from becoming a projectile or otherwise falling and causing damage to persons or property. As disclosed in the '408 patent, the opened portion of the vent may be attached to the structure, or to a vent frame installed in the structure, by a shock cord or cable. Alternatively in the '408 patent, the opened portion of the vent may be attached to the structure or vent frame by way of a hinge or other attachment mechanism.
In the known applications of vents, including burst panel vents, retaining an opened portion of the vent attached to the structure or vent frame may transfer relatively high forces to the structure as the opened portion of the vent opens. For example, a known burst panel vent is typically used with a high-strength enclosure that can survive a “reduced explosion pressure” (Pred)—i.e., the maximum pressure developed in a vented enclosure during a vented deflagration—of 1½ pounds per square inch gage (psig) or more. Such enclosures typically are constructed from reinforced concrete, bolted or welded steel fabrications, and fiber reinforced fabrications or a combination of materials to achieve the necessary operating strength. Even though the activation pressure (Pstat) of a vent used in such an enclosure may be lower than 1½ psig—typically ⅓ psig or less for large volume building structures—the pressure generated by a deflagration will continue to increase after the vent has opened due to the dynamic nature of a deflagration and/or combustion event; therefore, the strength of the enclosure elements that retain the vent must be sufficiently strong to survive an explosion using a known explosion vent. The force that must be carried by the enclosure at the vent location can be determined from the value of Pred and the vent area. For example, a vent might have a nominal size of 36-inches×36-inches, presenting a vent area of 1296 square inches. At a set pressure of ⅓ psig this could impart a load of 432 pounds on the vent-retaining element of the enclosure. However, the enclosure and/or vent-retaining element may be required to survive a Pred of 1½ psig—which could impart a force of 1944 pounds. In other applications, a Pred of 3 psig would impart a force of 3888 pounds. These are forces that can lead to failure of enclosure vent mounting arrangements. In a worst case scenario, a vent-mounting frame arrangement could be torn out of the enclosure under such high forces, presenting a secondary mechanical hazard.
It is desirable to enable safe venting of lower strength enclosures, such as sheet metal or simple masonry, which may not survive the Pred of the vent application. It also is desirable to enable venting where the mounting arrangement of a vent (e.g., the frame, bolts, and/or other mechanism(s) by which a vent is installed in a structure or enclosure) cannot otherwise cope with the momentary forces generated when a known vent activates in response to a deflagration. The forces generated on a mounting arrangement are a function of vent area and Pred. Thus, with large vent areas occupying several square feet, the combined loading of even a fraction of a psi of pressure can be considerable. Accordingly, it is desirable to provide a vent that will reduce the forces imparted on a mounting arrangement and/or enclosure when a large vent area opens in response to a deflagration. The present disclosure provides one or more of these, and/or other, advantages.